Method for polymerizing macrocyclic poly(alkylene dicarboxylate) oligomers

ABSTRACT

Macrocyclic polyester oligomers are converted to linear polyesters by contact at a temperature of about 160°-300° C. with a cyclic titanium catalyst such as di-(1-butyl)-2,2-dimethylpropane-1,3-dioxytitanate, bis(2,2-dimethyl-1,3-propylene) titanate or 1-(1-butoxy)-4-methyl-2,6,7-trioxa-1-titanabicyclo[2.2.2]octane. Such catalysts have high activity and produce linear or branched polyesters of very high molecular weight.

This application is a division of application Ser. No. 08/371,715, filedJan. 12, 1995, now U.S. Pat. No. 5,527,976.

BACKGROUND OF THE INVENTION

This invention relates to the polymerization of macrocyclic polyesteroligomer compositions. More particularly, it relates to an improvedmethod for such polymerization which is capable of producing novelbranched polyesters.

The preparation of macrocyclic poly(alkylene dicarboxylate) oligomersand their polymerization to linear polyesters is described in U.S. Pat.Nos. 5,039,783, 5,214,158 and 5,231,161 and in copending, commonly ownedapplications Ser. No. 08/369,986 now U.S. Pat. No. 5,466,744 and Ser.No. 07/978,583 now U.S. Pat. No. 5,321,117. The catalysts employed forsuch polymerization include various organotin compounds and titanateesters.

Polymerization using these catalysts is quite successful and affordspolyesters having excellent properties and a wide variety of potentialapplications. However, the catalysts are somewhat sensitive toimpurities present in the macrocyclic polyesters, particularly acidicimpurities which can include water, hydroxy compounds and carboxylicacids and their anhydrides.

In the presence of such impurities, the catalyst may be partiallydeactivated and polymerization may be incomplete or may yield polymerswith low weight average molecular weights. Attempts to increase polymeryield by increasing the proportion of catalyst in the polymerizationmixture cause significant further reductions in the molecular weight ofthe linear polymer, since the catalyst becomes part of the polymer endgroup and increased amounts of catalyst compete for the same proportionsof structural units in the macrocyclic oligomers.

In copending, commonly owned applications Ser. Nos. 08/262,793,08/262,795 and 08/262,799 now U.S. Pat. Nos. 5,386,037; 5,389,719, and5,387,666 respectively, there are disclosed several cyclic tin catalystswhich offer improvements with respect to the above-described problems.However, these tin compounds are expensive to prepare and there areenvironmental and health concerns about their use,

It would be desirable, therefore, to develop safe and inexpensivecatalysts with high activity for the polymerization of macrocyclicoligomers containing increased proportions of impurities, especiallyacidic impurities. It would be further desirable to provide a means forinexpensively converting macrocyclic oligomer compositions to branchedpolyesters having improved dimensional stability, for use asload-bearing members in automobiles and the like.

SUMMARY OF INVENTION

The present invention provides a method for producing polyesters of highmolecular weight and high dimensional stability from macrocyclicoligomers. Said oligomers and polyesters may be employed in thefabrication of fiber-reinforced composites and the like. The polyesterproducts include branched polyesters, whose proportion in the productmay be varied and which contribute to dimensional stability.

The invention in one of its aspects is a method for preparing apolyester which comprises contacting, at a temperature within the rangeof about 160°-300° C., at least one macrocyclic polyester oligomercomprising structural units of the formula ##STR1## wherein R¹ is analkylene or mono-or polyoxyalkylene radical containing a straight chainof about 2-8 atoms and A is a m- or p-linked monocyclic aromatic oralicyclic radical, with at least one titanium-containing macrocyclicpolyester oligomer polymerization catalyst having, at least in part, theformula ##STR2## wherein: R² is an alkyl radical, or the two R² radicalstaken together form a divalent saturated aliphatic hydrocarbon radical;

R³ is a C₂₋₁₀ divalent or trivalent saturated aliphatic hydrocarbonradical;

R⁴ is a methylene or ethylene radical; and

n is 0 or 1.

Another aspect of the invention is a polyester prepared by theabove-described method. Polyesters of this type have unique structuralcharacteristics, as explained in detail hereinafter.

Still another aspect of the invention is a titanabicyclo compound of theformula ##STR3## wherein R⁴ is as previously defined, R⁵ is hydrogen orC₁₋₇ alkyl and R⁶ is alkyl as defined for R².

DETAILED DESCRIPTION; PREFERRED EMBODIMENTS

The macrocyclic polyester oligomers which are polymerized according tothis invention may be prepared by contacting at least one diol of theformula HO--R¹ --OH and at least one diacid chloride of the formula##STR4## under substantially anhydrous conditions and in the presence ofa substantially water-immiscible organic solvent, with at least oneunhindered tertiary amine; said contact being conducted at a temperaturefrom about -25° to about +25° C. This procedure is described in detailin the aforementioned patents, and it is therefore deemed unnecessary toprovide a detailed explanation herein. In most instances, the productsare mixtures of macrocyclic oligomers having differing degrees ofpolymerization. The preferred oligomers in many instances arepoly(butylene terephthalate), poly(ethylene terephthalate) andcopolymers thereof.

According to the present invention, the macrocyclic polyester oligomersare converted to linear or branched polyesters, often of high molecularweight, by contact with a titanium-containing macrocyclic polyesteroligomer polymerization catalyst. The catalysts employed are thosehaving, at least in part, formula II. In that formula, the R² values maybe alkyl radicals, typically C₁₋₁₀ alkyl and especially primary andsecondary alkyl radicals. Also included are spiro compounds wherein theR² radicals together form a divalent saturated aliphatic hydrocarbonradical, typically identical to R³ as defined hereinafter.

The R³ value may be a divalent (when n is 0) or trivalent (when n is 1)saturated linear or branched, preferably branched, aliphatic hydrocarbonradical containing 2-10 and preferably 3-10 carbon atoms. It usually hasa chain of 2-3 and preferably 3 carbon atoms separating the oxygenatoms. R⁴, when present, is a methylene or ethylene radical; it shouldbe noted that when R⁴ is present the second R² O moiety attached totitanium is absent.

The following are typical of titanium compounds employed as catalystsaccording to the present invention: ##STR5##

Di-(1-butyl)2,2-dimethylpropane-1,3-dioxytitanate ##STR6##Di-(1-butyl)2,2-diethylpropane-1,3-dioxytitanate ##STR7##Di-(1-butyl)2-(1-propyl)-2-methylpropane-1,3-dioxytitanate ##STR8##Di-(1-butyl)2-ethylhexane-1,3-dioxytitanate ##STR9##Di-(2-ethyl-1-hexyl)2,2-dimethylpropane-1,3-dioxytitanate ##STR10##Di-(2-ethyl-1-hexyl)2,2-diethylpropane-1,3-dioxytitanate ##STR11##Di-(2-ethyl-1-hexyl)2-(1-propyl)-2-methylpropane-1,3-dioxytitanate##STR12## Di-(2-ethylhexyl)2-ethylhexane-1,3-dioxytitanate ##STR13##Di-(2-ethylhexyl)2-ethylhexane-1,3-dioxytitanate ##STR14##Bis(2,2-dimethyl-1,3-propylene)titanate ##STR15##Bis(2,2-diethyl-1,3-propylene)titanate ##STR16##Bis[2-(1-propyl)-2-methyl-1,3-propylene]titanate ##STR17##Bis[2-(1-propyl)-2-ethyl-1,3-propylene]titanate ##STR18##Bis(2-ethyl-1,3-hexylene)titanate ##STR19##1-(1-Butoxy)-4-methyl-2,6,7-trioxa-1-titanabicyclo[2.2.2]octane##STR20##1-(2-ethyl-1-hexoxy)-4-methyl-2,6,7-trioxa-1-titanabicyclo[2.2.2]octane##STR21## 1-(1-Butoxy)-4-ethyl-2,6,7-trioxa-1-titanabicyclo[2.2.2]octane##STR22##1-(2-ethyl-1-hexoxy)-4-ethyl-2,6,7-trioxa-1-titanabicyclo[2.2.2]octane##STR23##1-(2-Propoxy)-4-ethyl-2,6,7-trioxa-1-titanabicyclo[2.2.2]octane.

The titanium-containing catalysts of formula II wherein n is 0 and R² isalkyl are illustrated by formulas III-XI. They may be prepared by thereaction of substantially equimolar proportions of a tetraalkyl titanateand an alkanediol such as 2,2-dimethyl-1,3-propanediol,2,2-diethyl-1,3-propanediol, 2-methyl-2-(1-propyl)-1,3-propanediol or2-ethyl-1,3-hexanediol. By "substantially equimolar" is meant withinabout 5 mole percent of equimolar, any excess generally being of thediol. The reaction is normally conducted at reduced pressure in an inertatmosphere, typically nitrogen, with the removal by distillation ofalkanol which is formed as a by-product. The product is typically aliquid or paste.

The compounds of formula II in which the two R² radicals taken togetherare alkylene are spiro compounds, illustrated by formulas XII-XVI. Theymay be prepared similarly, except that the molar ratio of diol totetraalkyl titanate is 2:1 or slightly (e.g., up to about 5 molepercent)in excess. They are typically crystalline solids having meltingpoints above 200° C. and often above 300° C.

Bicyclo compounds wherein n is 1 are illustrated by formulas XVII-XXI.They may be obtained by the similarly conducted reaction ofsubstantially equimolar proportions of a tetraalkyl titanate and a triolof the formula ##STR24## wherein R³ and R⁴ are as previously defined,such as 2,2-bis(hydroxymethyl)-1-butanol or2,2-bis(hydroxymethyl)-1-pentanol. They are also typically crystallinesolids melting above 300° C.

As described hereinafter, it is frequently advantageous to employliquids rather than solids as catalysts. By the reaction of 2-3 moles oftetraalkyl titanate with 1 mole of triol, a mixed catalyst containingtetraalkyl titanate species and bicyclo species of formula II in which nis 1, of the type represented by formulas XVII-XXI, which is in liquidform at ambient temperatures, may be obtained. This is unexpected, sincesimple mixtures of the tetraalkyl titanate and the previously preparedtriol titanate are heterogeneous. Similar mixed catalysts in liquid formmay be obtained by the reaction of tetraalkyl titanate with a mixture ofdiol and triol, the molar ratios of tetraalkyl titanate to diol andtriol being about 1.2-2.0:1 and about 3-4:1, respectively.

The preparation of titanate compounds useful as catalysts is illustratedby the following examples.

EXAMPLE 1

A mixture of 7.810 grams (13.83 mmol.) of tetra-2-ethyl-1-hexyl titanateand 1.828 grams (13.83 mmol.) of 2,2-diethyl-1,3-propanediol was chargedto a 50-ml. three-necked flask equipped with a distillation adapter anda thin capillary as a nitrogen inlet. The mixture was stirred in anitrogen atmosphere for 1 hour at room temperature. The pressure wasthen reduced to 50 millitorr and the mixture was heated to 128° C. over1 hour, whereupon 2-ethyl-1-hexanol was removed by distillation. Theresidue was the desireddi-(2-ethyl-1-hexyl)2,2-diethylpropane-1,3-dioxytitanate, the compoundof formula VIII. The yield was 5.80 grams, or 96.1% of theoretical.

Similar methods were employed to prepare the compounds of formulasIII-VII and IX-XI. All were clear liquids except IV, which was a hazyliquid, and III, V and VII, which were pastes.

EXAMPLE 2

The apparatus of Example 1 was employed for the reaction of 5.448 grams(9.647 mmol.) of tetra-2-ethyl-1-hexyl titanate with 3.092 grams (19.29mmol.) of 2-(1-butyl)-2-ethyl-1,3-propanediol at 90° C. and a pressureof 50 millitorr. The viscous residue solidified upon cooling. It wastriturated with hexane to afford the desiredbis[2-(1-butyl)-2-ethyl-1,3-propylene]titanate, the compound of formulaXV, as a solid having a melting point of 314°-317° C. The yield was 3.33grams, or 94.7% of theoretical.

The method of Example 2 was also employed for the preparation of thecompounds of formulas XII-XIV, all of which were solids melting above330° C.

EXAMPLE 3

The procedure of Example 2 was employed for the reaction of 6.526 grams(19.18 mmol.) of tetra-1-butyl titanate with 5.608 grams (38.35 mmol.)of 2-ethyl-1,3-hexanediol at 90°-100° C. and 20 millitorr. The product,a white powder, was the desired bis(2-ethyl-1,3-hexylene) titanate, thecompound of formula XVI. It melted at 210°-230° C. and existed as astable colorless liquid at 235° C. The yield was 5.97 grams, or 92.6% oftheoretical.

EXAMPLE 4

The apparatus of Example 1 was employed for the reaction of 9.671 grams(17.12 mmol.) of tetra-2-ethyl-1-hexyl titanate with 2.373 grams (17.68mmol.) of 2,2-bis(hydroxymethyl)-1-butanol, at 0.5 millitorr underdistillation conditions. The desired1-(1-butoxy)-4-methyl-2,6,7-trioxa-1-titanabicyclo[2.2.2]octane, thecompound of formula XVII, was obtained as a white crystalline solid witha melting point of 360°-365° C. The yield was 4.96 grams, or 91% oftheoretical.

A similar method was employed for the preparation of the compounds offormulas XVIII-XXI, all of which were solids melting above 360° C. withdecomposition.

EXAMPLE 5

The apparatus of Example 1 was employed for the reaction of 32.056 grams(56.76 mmol.) of tetra-2-ethyl-1-hexyl titanate and 2.539 grams (18.92mmol.) of 2,2-bis(hydroxymethyl)-1-butanol (hereinafter "triol"), underdistillation conditions at 100 millitorr. There was obtained the desiredmixed titanate (hereinafter "catalyst XXII")in liquid form; the yieldwas 26.36 grams (96.9% of theoretical).

Similar products were prepared from mixtures of the following molarratios:

Catalyst XXIII--titanate/triol, 2:1;

Catalyst XXIV--titanate/triol,2.5:1;

Catalyst XXV--titanate/triol/2,2-diethyl-1,3-propanediol, 3:1:2;

Catalyst XXVI--titanate/triol/2-(1-propyl)-2-methyl-1,3-propanediol,4:1:3;

Catalyst XXVII--titanate/triol/-2-ethyl-1,3-hexanediol, 4:1:3;

Catalyst XXVIII--titanate/triol/2,2-diethyl-1,3-propanediol, 3:1:1.

All were liquids except XXIII, which was a paste.

According to the present invention, the macrocyclic polyester oligomersare converted to high molecular weight polyesters by contact at atemperature in the range of about 160°-300° C., preferably 160°-250° C.,with the titanium-containing macrocyclic polyester oligomerpolymerization catalyst. The latter is typically employed in the amountof about 0.01-2.0 and preferably about 0.05-1.0 mole percent based onstructural units in the oligomers. In the case of mixed catalysts suchas XXIII-XXVIII, the mole percentage calculation is on the basis of asingle titanium atom per molecule.

For use in such operations as liquid injection molding, the use ofliquid catalysts is preferred. If a non-liquid catalyst is employed fora polymerization, it may be conveniently introduced in solution in asuitable solvent.

The polyesters of this invention have high molecular weights even whenprepared from oligomer mixtures with a relatively high proportion ofacidic impurities. The titanium catalysts initiate polymerization byincorporating ester units between the oxygen and carbon atoms in theirmolecular structure. Thus, a catalyst of formula II wherein n is 0 willafford a polyester with an R³ moiety within the chain. When the catalystis a bicyclo compound (i.e., n is 1), the polyester has a branchedstructure. As a rule, the titanium remains in the polyester end groupbut is removed upon contact with moist air.

It is within the scope of the invention to employ a mixture of catalystsof formula II, or a mixture of such a catalyst with one of anotherstructure such as a tetraalkyl titanate, to produce a mixture ofbranched and linear polyesters. The proportions of the two types ofcatalysts may be varied to afford the desired degree of branching.

The method of this invention is illustrated by the following examples.All percentages are by weight. Molecular weights were determined by gelpermeation chromatography relative to polystyrene.

EXAMPLE 6

A 25-ml. two-necked flask equipped with a vacuum adapter and a nitrogeninlet was charged with 5 grams (22.7 mmol. based on structural units) ofmacrocyclic poly(butylene terephthalate) oligomers. The oligomers weredried by heating at 100° C. under vacuum for 1/2 hour, after which thetemperature was raised to 190° C. and stirred for 15 minutes to melt theoligomers. Nitrogen was passed into the flask to bring it to atmosphericpressure, after which 38.2 mg, (0.114 mmol., 0.5 mole percent) ofcompound XVI, in the form of an 18.6% solution in o-dichlorobenzene, wasinjected into the melt using a micro-syringe. The melt became veryviscous and the polymer crystallized within 10 minutes. The mixture wasmaintained at 190° C. for an additional 20 minutes and was then cooledto room temperature. It was the desired linear polyester and had weightaverage and number average molecular weights of 303,600 and 129,800,respectively.

EXAMPLE 7

Following the procedure of Example 6, 50 microliters (114 mmol.) ofcatalyst VIII as a liquid (without solvent) was injected into a 5-gramsample of macrocyclic poly(butylene terephthalate) oligomers andpolymerization was allowed to proceed. The product was a linearpolyester having weight average and number average molecular weights of111,200 and 35,200, respectively.

EXAMPLE 8

Following the procedure of Example 6, a mixed macrocyclic oligomermixture comprising 95 mole percent poly(butylene terephthalate) and 5mole percent poly(ethylene terephthalate) was polymerized by theaddition of a 17.2% solution in o-dichlorobenzene of catalyst XX. Theresulting branched polyester had weight average and number averagemolecular weight of 285,000 and 58,500, respectively.

EXAMPLES 9-14

Following the procedure of Example 7, macrocyclic poly(butyleneterephthalate) oligomers were polymerized to mixtures of linear andbranched polyesters by the addition of various catalysts in the amountof 0.5 mole percent. The results are given in the following table.

    ______________________________________                                        Example   Catalyst      Mw      Mn                                            ______________________________________                                         9        XXII          109,300 32,300                                        10        XXIV          124,100 37,700                                        11        XXV           151,800 43,100                                        12        XXVI          133,000 39,500                                        13        XXVII         127,300 39,600                                        14        XXVIII        135,500 39,700                                        ______________________________________                                    

In a control experiment conducted under identical conditions with theuse of tetra-2-ethylhexyl titanate, poly(butylene terephthalate) havingweight and number average molecular weights of 62,700 and 24,700,respectively, was obtained. Thus, the polyesters of the presentinvention have substantially higher molecular weights than polyestersprepared using tetraalkyl titanates.

What is claimed is:
 1. A method for preparing a polyester whichcomprises contacting, at a temperature within the range of about160°-300° C., at least one macrocyclic polyester oligomer comprisingstructural units of the formula ##STR25## wherein R¹ is an alkylene ormono-or polyoxyalkylene radical containing a straight chain of about 2-8atoms and A is a m- or p-linked monocyclic aromatic or alicyclicradical, with at least one titanium-containing macrocyclic polyesteroligomer polymerization catalyst having, at least in part, the formula##STR26## wherein: R² is an alkyl radical, or the two R² radicals takentogether form a divalent saturated aliphatic hydrocarbon radical;R³ is aC₂₋₁₀ divalent or trivalent saturated aliphatic hydrocarbon radical; R⁴is a methylene or ethylene radical; and n is 0 or
 1. 2. A methodaccording to claim 1 wherein R² is C₁₋₁₀ primary or secondary alkyl. 3.A method according to claim 2 wherein n is
 0. 4. A method according toclaim 2 wherein n is
 1. 5. A method according to claim 4 wherein R⁴ ismethylene.
 6. A method according to claim 2 wherein R³ is a C₃₋₁₀radical.
 7. A method according to claim 6 wherein R³ has a chain ofthree carbon atoms separating the oxygen atoms.
 8. A method according toclaim 1 wherein the R² radicals together form a C₃₋₁₀ saturatedaliphatic hydrocarbon radical.
 9. A method according to claim 8 whereinthe two R² radicals form a branched hydrocarbon radical.
 10. A methodaccording to claim 1 wherein the macrocyclic polyester oligomer ismacrocyclic poly(ethylene terephthalate), macrocyclic poly(butyleneterephthalate) or a copolymer thereof.
 11. A method according to claim 1wherein the proportion of catalyst is about 0.01-2.0 mole percent basedon structural units in the oligomers.
 12. A method according to claim 1wherein the catalyst contains tetraalkyl titanate species and bicyclospecies of formula II in which n is 1, and is prepared by the reactionof 2-3 moles of a tetraalkyl titanate with 1 mole of a triol of theformula ##STR27##